Anti-neutrophilic cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a group of autoimmune conditions marked by the immune system erroneously attacking small blood vessels in various organs and tissues, causing inflammation and damage to those small vessels.
This immune attack is triggered by the presence of self-reactive antibodies called ANCAs, which attach to immune neutrophils (a type of white blood cell, important to fighting infections) and wrongly activate them to induce an immune response. ANCAs typically target one of two proteins, proteinase 3 (PR3) or myeloperoxidase (MPO).
Depending on the affected organs, AAV is grouped into three main types: microscopic polyangiitis, granulomatosis with polyangiitis, and eosinophilic granulomatosis with polyangiitis. In the rare instances in which vasculitis is observed in the kidneys alone, patients have a form of disease called renal-limited vasculitis.
Knowing which AAV subtype a patient has is key to determining the best course of treatment. But other factors, such as antibody type (PR3 or MPO), severity of symptoms, and how fast the disease is progressing are also considered.
Microscopic polyangiitis (MPA)
MPA, the most common type of AAV, can be distinguished from the other subtypes by the lack of granulomas — masses of immune cells — at the site of inflammation.
This disease type can affect people of all ages and ethnic backgrounds, although it was found to be more common among middle-age whites in the U.S. A majority of patients (55%) carry MPO-ANCAs, or antibodies against the MPO protein.
The disease commonly causes damage to the small vessels in the kidneys (in about 80% of patients), but other symptoms, such as skin lesions, nerve damage, and weight loss are also common. Fevers frequently occur in more than 55% of MPA patients.
Capillaries in the lungs can be damaged to the point where bleeding occurs in the air sacs (alveoli) where gas exchange takes place, a potentially life-threatening event with patients coughing up blood. Symptoms due to inflammation can also involve the eyes, muscles, and joints.
Granulomatosis with polyangiitis (GPA)
Similar to MPA, the GPA subtype can also result in inflammation in various tissues, but patients typically have a classic triad of lung, kidney, and upper respiratory tract (nose, trachea, and ears) involvement.
Respiratory tract symptoms are seen in 70% of the patients, and may include ear infections, or reduced hearing abilities, inflammation in the eye, a runny nose, nose pain, nosebleeds, and shortness of breath. Patients can also develop pulmonary infiltrates or nodules.
Inflammation sites in GPA patients normally have granulomas and necrotic regions (areas of dying cells). A chronic nose infection with Staphylococcus aureus, found in over 60% of patients, has been suggested as a possible GPA trigger.
This AAV subtype generally is first evident in mid-life (around age 40) and is slightly more common to men, but it can affect people of any sex and age. About 75–90% of GPA patients have autoantibodies against PR3 (PR3-ANCA).
Eosinophilic granulomatosis with polyangiitis (EGPA)
EGPA, formerly called Churg-Strauss syndrome, is typically limited to the lungs and gastrointestinal tract, although other organs, like the heart and kidneys, can also be affected. It is caused by granulomas primarily made up of eosinophils, another type of white blood cell of the immune system. Nearly all patients have more than 10% of eosinophils in the blood (levels above 5% are generally considered elevated).
People with undiagnosed EGPA may experience asthma-like symptoms, and possibly nasal polyps and allergic rhinitis (also known as hay fever), sometimes years before other symptoms of vasculitis appear.
Symptoms that may develop with time include tingling, numbness, shooting pains, and muscle degradation in the hands and/or feet. Some symptoms associated with damage to the lungs, kidneys, and skin are similar to those of people with GPA.
This type of the disease is more common in men and the age of onset ranges from 15 to 70.
In this form of AAV, patients experience inflammation in the capillaries forming the glomeruli, which are the filtering units of the kidneys. The inflammation leads to tissue scarring and permanent damage that ultimately cause kidney failure.
This means the kidneys are unable to remove toxins and waste from the blood, leading to a need for dialysis or a kidney transplant.
Renal-limited vasculitis is also characterized by scattered cell death in the kidneys, formation of crescents — masses of proliferating cells, mostly immune cells, that are a marker of severe injury — in the glomeruli, and the few or no antibody deposits in the kidney (the so-called pauci-immune vasculitis).
Last updated: May 19, 2021
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